have any repairs been attempted? Are you saying you have a misfire also?
I suspect leaking head gaskets, numbers 1 & 4 are notorious for leaking. Pull those plugs and check for any shade of green on the electrodes, if they are case closed, it's head gaskets. Otherwise check the performance of the heater on a highway run of 15-20 miles, if you lose heat output, its air locking and its head gaskets. Finally you could do the block test with the blue fluid, but these tend just to dribble in coolant and not the produce much exhaust gas. Put a pressure tester on cooling system stone cold and rev engine to 3000 rpm see if you have a abnormal pressure increase. You must absolutely rule this out before proceeding. Get back with me with the resluts.
I am interested in the Temp of the heat, put it on vent and hold you hand up to it driving down the freeway on all the way heat, blower on high. [open the windows I know your in Florida] It should burn your hand to keep holding it there. See if it changes to where you can keep your hand there because its only luke hot.
Here is the info on IMRC...
The air induction system improves engine performance by using the intake manifold runner control (IMRC) assemblies as follows:
The valve plates are opened and closed by the IMRC vacuum actuator, which is controlled by the:
Above 2950 rpm:
Need to snap throttle open to get above 3500 rpm and watch the runner levers [9S514 in pict] to see if they move from stop to stop. They probably move and need replacement, [bad sensors inside] if not check the vacuum source to them.
Remove E-clip retaining vacuum control linkage to lever/shaft assembly.
Remove adjustment screw from the vacuum control (9S514) and bracket.
Remove two bolts retaining IMRC vacuum control and bracket to IMRC housing assembly.
Disconnect linkage from the lever/shaft assembly and remove vacuum control.
To install vacuum control and bracket assembly, reverse Removal procedure. Tighten retaining bolts to 8-11 Nm (6-9 lb-ft). Adjust vacuum control as outlined.
Hi, I'm sorry if I offended you, most people asking questions here are not techs.
So tell me exactly what you still need help with, and I promise I won't mention head gaskets again!
Have you replaced the runner motors? Is that problem resolved?